Trouble Installing Graphics Card

Hello,

I am having troubles installing my NVIDIA GeForce 8500 GT graphics card. I have had it for years but for some reason it uninstalls itself and the graphics card rolls back to the default one. I have tried many of times installing it using proper driver disk and downloading them from nvidia.com. The messages I am getting are:

'Setup detected that the operating system in use is not Windows Vista [32-bit]. This setup program and its associated drivers are designed to run only on Windows Vista [32-bit]. The installation will be terminated.'

AND

'The NVIDIA setup program could not locate any drivers that are compatible with your current hardware. Setup will now exit.'

However, my system is running on 32-bit and I have checked multiple times and I know my graphics card is there because it was only yesterday I was playing a game which needed it.

Any help would be greatly appreciated, Thanks!